Computers and other peripheral devices often connect to one another through universal serial bus (USB) or IEEE 1394 cables and connectors. These cables and connectors are known as versatile interfaces for data transmission. They may be employed in conjunction with controllers for HVAC systems, burners, fuel cells, cogeneration (combined heat and power) plants, etc.
USB cables commonly provide a pair of leads for data transmission. They are labeled D+ and D− throughout this disclosure. The nominal operating range of the D+ and D− leads is 0-3.6 V. They ought to remain undamaged up to the 4.4 V-5.25 V range when shorted to an overvoltage condition. In addition to the wires for data transmission, another pair of leads is provided to supply power. These leads are labeled VBUS and GND throughout this disclosure. The VBUS lead typically operates at voltages of 5 V DC whereas the GND lead of the system may connect to earth. The D+, D−, VBUS, and GND leads form a total of four leads in a standard (USB) cable.
Transceiver interface circuitry such as USB circuitry or IEEE 1394 circuitry is prone to damage due to electrostatic discharge (ESD). Actually, electrostatic discharges may cause damage not only to the interface circuitry but also to any computing or electronic devices connected thereto. Due to triboelectric charging, electrostatic discharges are omnipresent and inhibition of and/or protection from any adverse effects on electronic circuitry is crucial. Electrostatic discharges generally occur when two objects come into contact after a build-up of electrostatic charge. These discharges typically decay within 100 microseconds. In spite of short duration, electrostatic discharges are known to cause damage to electronics equipment even at peak voltages as low as 50 V.
Transceiver interface circuitry such as USB circuitry or IEEE 1394 circuitry is also prone to damage due to ground faults. Normally, the plugs and the sockets of a USB cable connection are mechanically arranged so as to inhibit ground faults. Ground faults may still occur, however, e.g., between pairs of computing devices connected via a USB cable. If each controller is supplied by transformer and the windings of those transformers connect terminals with opposite polarities to ground, the ground potentials of these devices will be unbalanced. A cable or a lead connecting the ground potentials of the two computing devices may then short-circuit the different ground potentials. A short-circuit along the leads of the cable may entail currents and/or current surges that jeopardize the inner components of the computing devices such as (MOSFET) transistors, capacitors, universal asynchronous receiver/transmitter circuits, etc.
A ground fault may not only result in excessive currents along the GND lead of a cable or connector. A ground fault may also cause an abnormal voltage drop between the VBUS lead at the first end of a connection and the GND lead at the second end of the connection. It is then desirable to break any current along the VBUS lead in order that the VBUS terminals at either side of the cable are disconnected. In addition, the D+ and the D− leads between either side of the connection should be interrupted. The electrical disconnection between the terminals inhibits adverse effects of excessive voltages and/or currents on (parts of) the circuitry.
From an electrical point of view, it is desirable to first establish a connection between the GND terminals on either side of a cable connection. The D+ and D− leads for data connection are subsequently connected. The plugs and the connectors used in the connection may, however, be dirty or defective. If the connections between the terminals on either side do not connect in sequence, abnormal currents may result. Those abnormal currents may impair the quality of the data connection and/or cause damage to the (transceiver interface) circuitry.
Document US2012/250204A1 was published on 4 Oct. 2012. US2012/250204A1 discloses a protection circuit and an input/output circuit. US2012/250204A1 describes a solution with separate switches CP1 and CP2. First switch CP1 produces an interruption signal when the voltage of a VBUS line exceeds a threshold. Second switch CP2 produces an interruption signal when the voltage of a VBUS line is below another threshold.
Document US2008/186644A1 was published on 7 Aug. 2008. US2008/186644A1 teaches a method of forming an over-voltage protection circuit and structure therefore. US2008/186644A1 teaches a first circuit 28 and a second circuit 41.
Document US2013/107409A1 was published on 2 May 2013. Also, US2013/107409A1 discloses a device and a process for protection against excessive voltage and/or current in systems having USB connections and the like.
Yet another document EP2677616A1 was published on 25 Dec. 2013. EP2677616A1 teaches an interface unit comprising an overcurrent and overvoltage protection device.